Australian basketball star Josh Giddey is being investigated by US police following social media allegations of an inappropriate relationship with an underage girl.

The Newport Beach Police Department in California said detectives had started an investigation into the accusations against Giddey, who plays for Oklahoma City Thunder.

“The Newport Beach Police Department is aware of information being circulated online involving an alleged relationship between professional basketball player Josh Giddey and a female minor,” a statement read.

“The Newport Beach Police Department is actively seeking additional information related to these allegations and pursuing all leads and evidence to obtain the facts of the case.”

It follows an anonymous social media post last week that alleged a girl seen with the 21-year-old Melbourne-born basketballer in videos and photographs was a high school junior at the time.

A high school junior in the US is typically aged 16 or 17. The age of consent in California is 18.

The social media account has since been deactivated.

TMZ reported on Thursday (AEDT) that police wanted to speak to the teenager. She and her family are said to be refusing to cooperate with the investigation.

The NBA said last week that it was also investigating. Giddey has declined to comment.

“I understand the question obviously, but no further comment right now,” he said last week.

“I get the question guys, I completely understand you want to know about it, but just for right now, I don’t have anything to say.”

OKC coach Mark Daigneault also refused to comment before Tuesday’s In-Season tournament game at Minnesota, which the Thunder lost 106-103.

“Personal matter,” Daigneault said. “I have no comment on that and that will be my answer on anything related.”

Giddey was targeted throughout the game by vociferous Timberwolves fans who jeered the young Boomers star whenever he touched the ball.

The Melburnian enjoyed 28 minutes of court time for 10 points, six rebounds and one assist.

Giddey is averaging 12 points, 5.8 rebounds and 4.5 assists per game for an Oklahoma City team that is off to a 11-6 start. He has started both games since the accusations emerged – both ended in losses.

He was the youngest NBA player to record a triple-double – at 19 years and 84 days – and the first player since Hall of Fame member Oscar Robertson in 1961 to record three consecutive triple-doubles as a rookie.

Giddey was the No.6 overall pick in the 2021 draft and was named to the All-Rookie second team during the 2021-2022 season. Last season, he averaged 16.6 points, 7.9 rebounds and 6.2 assists.

At the World Cup this past northern hemisphere summer, he averaged a team-high 19.4 points for an Australia team that went 3-2.

The 2021 NBL rookie of the year is a key part in the Boomers’ hopes of improving on their historic bronze medal in Tokyo at next year’s Paris Olympics.

– with AAP